1. Field of the Invention
The present invention relates to a pressure-sensitive sheet recording system. It more particularly relates to a pressure-sensitive recording system in which formation of smudge is prevented. "Smudge", as used herein, means the undesired colored product of reaction between a colorless, color-forming, material contained in microcapsules and a polymeric color-developing material, wherein the smudge is a result of incidental or accidental microcapsule rupturing contact. Smudge resistance is accomplished, in the present invention, by careful selection of solvents and careful arrangement of component materials.
2. Description of the Prior Art
U.S. Pat. No. 3,576,660 issued Apr. 27, 1971 discloses a smudge-resistant, pressure-sensitive sheet wherein there is an encapsulated, acid-reactive, chromogenic material in liquid solution and an encapsulated acid reactant in liquid solution. The two liquid solutions are contained in different kinds of capsules and are coated together onto sheet substrates. Smudge resistance is achieved, in that patent disclosure, by taking advantage of the different component releasing character of the two kinds of capsule walls.
U.S. Pat. No. 3,617,334 issued Nov. 2, 1971 discloses a smudge-resistant, pressure-sensitive sheet of a coating of encapsulated, acid-reactive, chromogenic material in liquid solution. The sheet is to be used with another surface containing the acid reactant. Smudge resistance is achieved, in that patent disclosure, by providing capsules which contain only diluent solvent in addition to the microcapsules containing chromogenic dye material. The diluent-containing capsules are provided in larger size than those containing dye; and the diluent-containing capsules are said to protrude above the dye-containing capsules in any capsule coating. Incidental, normally-smudge-producing, forces tend to contact only the larger capsules and be buffered away from the smaller capsules. The diluent capsules are solely for pressure buffering purposes and have contents-selected to have no effect on the color-producing components of the sheet.
U.S. Pat. No. 3,738,857 issued June 12, 1973 discloses a smudge-resistant, pressure-sensitive sheet wherein there are, both, encapsulated chromogenic material and encapsulated diluent material. The chromogenic material and the diluent material are encapsulated as individual, finely-divided, droplets aggregated together to yield a capsule unit of both kinds of materials separated, but present in the same capsules. The droplets of diluent are provided in larger size than droplets of the chromogen; and the diluent droplets serve as force buffers in much the same way as discussed in the previous paragraph.